Video content may be transmitted over links with unknown or variable bandwidth characteristics. To accommodate the different bandwidths that may be available, the video content may be offered in several formats, each with different bandwidth requirements. If the quality of a communication link degrades during delivery such that the selected format is no longer supported, a server may stop transmitting the selected format and select a format with lower-bandwidth requirements for transmission. Varying the format of a video stream over time is known as adaptive streaming. A need exists for systems and methods that enable adaptive streaming that are modular, scalable, and efficient.